Manufacture of polycarboxylic acids



Patented May 26, 1953 UNITED STATES PATENT OFFICE 2,640,075 MANUFACTUREOF POLYCARBOXYLIC ACIDS Martinus L. Goedkoop, Geleen, Netherlands, as-

signor to De Directie van de Staatsmijnen in Limburg, handelend voor ennamens de Staat der Nederlanden, Heerlen, Netherlands No Drawing.Application March 26, 1951, Serial No. 217,679. In the Netherlands April1, 1950 Field of invention It is known that when carbonaceous materialsare oxidized with nitric acid, oxidation products can be obtainedtherefrom which contain benzene polycarboxylic acids. When anthracite orcoke is used in this operation as the initial material, the benzenepolycarboxylic acids chiefly is mellitic acid from which pyromelliticacid or its anhyride can be prepared by heating.

In U. S. patent application No. 182,143, filed August 29, 1950, now U.S. Patent No. 2,576,020, by J. Knops, a process has been described formanufacturing pyromellitic acid by heating the higher polycarboxylicacids in a fluidized state by means of water vapor with the initialmaterial subdivided, preferably by being fixed to a finegrained, porouscarrier. When coke breeze is used in this operation as the carrier, amixture of coke and carbonizable substance is left as a fluidizationresidue. This solid residue from the heating operation in the past hasbeen discarded as a useless by-product.

Objects A principal object of this invention is the provision of newimprovements in known methods for the manufacture of polycarbo'xylicacid, especially mellitic acid and pyromellitic acid by the oxidation ofcoke. Further objects include:

i. The provision of new steps in such procedures which make .possiblethe savings of reacting materials.

2. The provision of improvements in such operations which make itpossible to carry them out in a continuous cyclic manner. I

3. The use of a new type of carbonaceous materials for oxidation to formaryl polycarboxylic acids which give high yields of desired productsand, at the same time, utilizing a material which has been considered awaste product heretofore.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

General description These objects are accomplished according to thepresent invention by a combination of procedural steps which includeforming or otherwise providing a quantity of an aryl polycarboxylicacid, coating coke breeze with said acid mixture, heating the coatedcoke breeze in a stream "0f gas containing water vapor to a temperaturebetween 250 and 400 C., recovering the solid residue which results fromsaid heating operation after passage of the gas stream thereover, andthen oxidizing said solid residue to form a mixture of arylpolycarboxylic acids containing mellitic acid, and recovering themixture of acids from the oxidized solid residue.

In the preferred form of the new procedures, the water vapor-containinggas stream is passed about the coated coke breeze at such a velocitythat the solid particles become fluidized the gas stream, the gas streamcoming off of the solid particles is treated to condense water vaportherefrom and pyromellitic acid is recovered irom the condensate, andthe oxidation of the solid residue resulting from the heating operationis accomplished by mixing the solid residue with nitric acid and heatingthe mixture.

Example The invention is further explained in the .following example of[actual operation in accordance with the invention.

To a hot solution of polycarboxylic acids which contains about g. ofthese acids per litre, said solution having been obtained by oxidizingcoke breeze with nitric acid, coke breeze (grain size 0.1-1.5 mm.) isadded in an amount of 850 g. per litre. The mixture is subsequentlydried and introduced into a fluidizing apparatus. The inn-- idization iscarried out at a temperature of 280 to 290 C. by means of preheatedsteam. The pyromellitic acid is entrained by the Water vapor escapingfrom the fluidizing apparatus. The condensate is cooled and acidulatedwith hydrochloric acid as a result of which an almostw'hite precipitateof raw pyromellitic acid is obtained. 150 g; raw polycarboxylic acidsgive a yield 01*"63 g. "pyro'mellitic acid.

The fiuidization residue which, in addition to coke, still contains someacidic materials, is transferred to an oxidation reactor and oxidized byheating with nitric acid. A reaction product is formed which yields, byfiltration, a solution of polycarboxylic acids which is subsequentlytreated in the manner described above.

Detailed description The aryl polycarboxylic acid mixture referred toabove can consist almost wholly of mellitic acid or may contain largerproportions of other acids in addition to mellitic acid. After thesolution obtained by oxidation with nitric acid is freed of undissolvedcomponents, the coke breeze is added to the solution and the mixture isthen dried by vaporization.

The resulting coated coke breeze can be heated to the necessarytemperature of 250 to 400 C. in a variety of ways. For example, it canbe charged into a rotary, inclined, cylindrical reactor and heated bypassing the water-vaporcontaining gas stream over the coated particles,while they ar agitated by rotation of the vessel. Preferably, however,the coated particles are charged into a vertical, cylindrical containeror the equivalent thereof, and the gas stream passed upwardly throughthe contained particles at such 'a velocity that the particles becomefluidized therein. In such a case, the gas stream is preheated to thetemperature necessary to raise :the particles within the temperaturerange speci- The gas stream which issues from the heated particles ofcoated coke breeze can be handled in a variety of ways, but preferably,is treated for the recovery of pyromellitic acid. 'This is most easilyaccomplished by condensing the water vapor in the gas stream, e. g., bycooling and then recovering the pyromellitic acid from the condensedwater.

The time of passage of the heated gas stream over the coated particlesis not critical and will depend to some extent upon the nature of thecoating and the amount of coating relative to the coke breeze. For mostefficient operation, this gas passage and heating operation should beconducted until the quantity of pyromellitic acid, issuing with thewater vapor in the gas stream, is too low for practical continuation ofthe operation. When a batch-type procedure is employed, the solidresidue at this point is removed and transferred to the next stage inthe process, namely, oxidation to form a mixture of aryl polycarboxylicacids. While this oxidation can be accomplished in a variety of ways, itis "preferably accomplished by mixing the solid residue with nitric acidand then heating, such as to the boiling point, to oxidize the solidmaterial to form a solution of aryl polycarboxylic acids which willcontain a large percentage of mellitic acid.

The coke breeze can be advantageously used in the same form in which itis obtained in normal commercial operation. On the other hand, ifdesired, the coke breeze may be further treated so as to obtain a veryuniform particle size which, preferably, is between 0.1 and 2 mm.

The coating of the coke breeze with the mixture of polycarboxylic acidor mellitic acid can be accomplished in any desired fashion.Advantageously, the coke breeze is coated by mixing it with the solutionof polycarboxylic acids resulting from the nitric acid oxidation andevaporating the mixture to form a solid subdivided material. 0n theother hand, the acid mixture can be concentrated to a molten state andthe coke breeze mixed with the melt. The impregnated coke breeze neednot be thoroughly dried since it may be used in the heating step in a,humid condition.

The proportion of coke breeze to acid mixture used in forming the coatedparticles is not critical and may be varied to accommodate thecharacteristics of the acid mixture or the treating apparatus. However,for most operation and, particularly, when fiuidization is employed, thecoke breeze should be between 1 and 3 times by weight of thepolycarboxylic acid mixture.

Conclusions The invention, as described above, provides certain newimprovements in the generally known method of forming mellitic acid andpyromellitlc acid or its anhydrate from solid carbonaceous material. Byusing these new improvements, 8. high efliciency of operation isobtained because of full utilization of all reacting materials andelimination of useless by-products. At the same time, the newimprovements make it possible to carry out a completely continuousoperation in which reactants from one stage are passed continuously to asubsequent stage.

I claim:

1. A process for the manufacture of polycarboxylic acids which comprisesproviding a quantity of an aryl polycarboxylic acid mixture containingmellitic acid obtained by oxidation of coke, coating coke breeze withsaid acid mixture, heating the coated coke breeze in a gas streamcontaining water vapor to between 250 and 400 C. whereupon the melliticacid in said mixture is converted to pyromellitic acid, the latter beingvolatilized by said gas stream and recovered therefrom, recovering thesolid residue comprising coke breeze and residual products derived fromsaid acid mixture, from said heating operation, oxidizing said solidresidue and recovering a mixture of polycarboxylie acids containingmellitic acid therefrom, and thereafter utilizing the recovered acidmixture for coating said coke breeze.

2. A process for the manufacture of mellitic acid and pyromellitic acidwhich comprises forming a mixture of aryl polycarboxylic acids con--taining mellitic acid by oxidation of coke, coating coke breeze withsaid mixture, fluidizing said coated coke breeze in a'water vaporcontaining gas stream, heating the coated material to a temperature ofbetween 250 and 400 C. while fluidized in said gas stream, condensingwater vapor from said gas stream subsequent to separation from thecoated material and recovering pyromellitic acid therefrom, recoveringthe solid residue from said heating operation, said residue comprisingcoke breeze and residual products derived from the acid mixtureundergoing treatment, mixing said residue with nitric acid, heating theresultin acid mixture to oxidize said solid residue including theresidual products included therein to obtain a solution ofpolycarboxylic acids containing mellitic acid from said heated reactionmixture and utilizing the thus obtained polycarboxylic acids for coatingsaid coke breeze.

3. A process as claimed in claim 1 wherein the coke breeze is between 1and 3 times by weight 5 of said polycarboxylic acid mixture with whichNumber it is coated. 2,555,410 MAR'I'INUS L. GOEDKOOP. 2,576,020

References Cited in the file of this patent 5 UNITED STATES PATENTS gNumber Name Date 1, 3 1,332,028 Coblentz et a1 Feb. 24, 1920 879'1822,176,348 Juettner Oct. 17, 1939 10 2,461,740 Kiebler Feb. 15, 1949 NameDate Howard June 5, 1951 Knops Nov. 20, 1951 FOREIGN PATENTS CountryDate Great Britain of 1907 Germany Mar. 4, 1927 France Feb. 16, 1943

1. A PROCESS FOR THE MANUFACTURE OF POLYCARBOXYLIC ACIDS WHICH COMPRISESPROVIDING A QUANTITY OF AN ARYL POLYCARBOXYLIC ACID MIXTURE CONTAININGMELLITIC ACID OBTAINED BY OXIDATION OF COKE, COATING COKE COKE BREEZE INA GAS STREAM HEATING THE COATED COKE BREEZE IN A GAS STREAM CONTAININGWATER VAPOR TO BETWEEN 250* AND 400* C. WHEREUPON THE MELLITIC ACID INSAID MIXTURE IS CONVERTED TO PYROMELLITIC ACID, THE LATTER BEINGVOLATILIZED BY SAID GAS STREAM AND RECOVERED THEREFROM, RECOVERING THESOLID RESIDUE COMPRISING COKE BREEZE AND RESIDUAL PRODUCTS DERIVED FROMSAID ACID MIXTURE, FROM SAID HEATING OPERATION, OXIDIZING SAID SOLIDRESIDUE AND RECOVERING A MIXTURE OF POLYCARBOXYLIC ACIDS CONTAININGMELLITIC ACID THEREFROM, AND THEREAFTER UTILIZING THE RECOVERED ACIDMIXTURE FOR COATING SAID COKE BREEZE.